The present invention relates to a device for pumping paint comprising a pump house adapted to receive paint from a paint source, a pump shaft for driving a pump member to rotate inside the house for pumping paint therethrough, said pump shaft being connected to an output shaft of a motor located outside the pump house through an intermediate shaft piece through a wall of the pump house, said motor being arranged to drive the pump shaft and thereby the pump member, as well as a sealing member adapted to counteract leakage of paint out from the pump house along the pump shaft.
xe2x80x9cPaintxe2x80x9d is here to be interpreted broadly and comprises all types of paints, with a colour as well as colourless ones, and with arbitrary bases, for example on solvent or water base.
Devices of this type are used for example for pumping paint to a spray nozzle for application of paint on an object, in which this pumping often takes place at a well defined dosing. In order to exemplify but not in any way restrict the invention it may be mentioned that pumps of this type, preferably gear pumps, are used for dosed paint feeding to spray nozzles of robots for spray application of paint on vehicle bodies and suchlike.
Paints have quite particular properties, which put quite particular demands on said sealing members of a device defined in the introduction. It is very important that this sealing member achieves a good sealing, since paint leaking may solidify and constitute a resistance against the rotation of the shafts or even prevent such a movement due to sticking of parts together when the pump does not move. Furthermore, paint leaking out from the pump house may be difficult and unpleasant to take care of. Different sealing members, which seals radially against the pump shaft have been suggested for this type of pumping devices for closing very tight against the pump shaft, but these sealing members have, to the extent that they have succeeded to obtain a sufficient degree of sealing, a too high friction against the pump shaft or surrounding parts of the wall of the pump house, depending upon whether they are non-rotating or rotate with the pump shaft, which has led to unnecessary energy losses, at the same time as the sealing member or the washer gets a shorter life time. The sealing members already known are then not so durable and excerted to wear as desired.
It may be mentioned that such sealing members are usually constituted by packing boxes or lip packings bearing against the pump shaft in the radial direction. These have a comparatively high friction and a too large leakage combined with a short life-time. Furthermore, the packing boxes require readjustment. Another disadvantage of the sealing members already known is that the structural material thereof cannot stand that paint particles come in between the sealing surfaces without degradation thereof.
The object of the present invention is to provide a device of the type defined in the introduction, which has a sealing, in which the disadvantages mentioned above of pumping devices already known are considerably reduced.
This object is according to the invention obtained by arranging the sealing member of such a device to bear sealingly in substantially axial direction against substantially axial surfaces of the pump shaft around this shaft, and that at least the sealing member or the axial surfaces are of a ceramic material.
By constructing at least one of the surfaces bearing against each other and the sealing member of a ceramic material a low friction between the sealing member and the parts moving with respect thereto may be obtained, so that a low motor power will be needed. An additional advantage of such a sealing is that the ceramic material may resist paint particles entering between the sealing surfaces while not being destroyed in any way. In the case that the sealing member is of a ceramic material it will be very durable to wear and according gets a long lifetime, and no readjustments are required either. Furthermore, a desired good tightness around the pump shaft is obtained.
According to a preferred embodiment of the invention the sealing member and the axial surfaces are of a ceramic material. This amplifies the advantages of the invention mentioned above.
According to another preferred embodiment of the invention said substantially axial surfaces are arranged on a portion of the pump shaft having an enlarged cross section and directed substantially in the direction of the pump shaft away from the pump house. The ceramic sealing member may in this way be comfortably arranged while carrying out an axial sealing action.
According to another preferred embodiment of the invention the device comprises members adapted to keep the sealing member pressed while bearing under pretension against said substantially axial surfaces. Thanks to the arrangement of such a pressing member, which according to another preferred embodiment of the invention may be a spring element, an optimum sealing function is obtained.
According to another preferred embodiment of the invention the device comprises members for radial pressing under pretension of the sealing member against the pump shaft, and according to a further development of this embodiment said member for radial pressing under pretension is an O-ring pretensioned by being arranged around the sealing member stretched with respect to a rest position. The axial sealing is in this advantageous way supplemented by a radial sealing with respect to the pump shaft under low friction.
According to another preferred embodiment of the invention said pump house wall has a space carried out in the direction of the pump shaft from the pump house towards the output shaft of the motor downstream of the sealing member, and a member is adapted to bring a lubricant, such as oil, to flow into, through and out of this space for flushing away or preventing a binding action on parts of the pump shaft and the house wall being movable with respect to each other of paint entering the space as a consequence of leakage from the pump house past the sealing member. It may hereby be prevented that paint solidifies and binds parts movable with respect to each other together and in such a way will cause shut down, at the same time as the lubricant applied will reduce the wear on such parts.
According to another preferred embodiment of the invention the device is adapted for dosed pumping of paint, and more particularly for dosed pumping of paint to a spray nozzle for spray application of paint on objects, which is a very advantageous application of the device according to the invention.
According to yet another preferred embodiment of the invention the device comprises a gear pump, which is the type of pump that has turned out to be the most advantageous for exactly dosed feeding of paint for spray application while maintaining shearing forces acting upon the paint on an acceptably low level.
Further advantages as well as advantageous features of the invention appear from the following description and the other dependent claims.